Psalms 97:1-2
The LORD Reigns
The LORD reigns, let the earth rejoice;
let the many coastlands be glad!
Clouds and thick darkness are all around him;
righteousness and justice are the foundation of his throne.

Righteousness and justice in the Old Testament come from the same root word.  They are indistinguishable from each other.  God is righteous and He is just.  And because God is one being, His attributes (which we separate into  individual parts in order to understand them) are not separate in God.  His attributes are never in conflict with each other.  His mercy and love never quarrel with His justice.

The Bible teaches us that we were all born in sin and therefore deserve the punishment of God - death.  Only the atoning work of Jesus can change that.  God’s justice is perfect.  We either receive life by being justified through faith, or we receive death if we live for sin.  For those that have received life, Jesus said the following: 

John 10:28-30
“I give them eternal life, and they will never perish, and no one will snatch them out of my hand. My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand. I and the Father are one.”

Father, praises to You for your justice is perfect.  Jesus, praises to You for the cross that gives life to sinners like me.  Forgive me for ever questioning the justice of God.  I pray these things in the matchless name of Jesus.  Amen.